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Questions and Answers
Which characteristic contributes to the hygiene of stainless steel?
Which characteristic contributes to the hygiene of stainless steel?
Aluminum serves as a protective layer against corrosion in its natural state.
Aluminum serves as a protective layer against corrosion in its natural state.
False
What is the primary purpose of anodization in aluminum processing?
What is the primary purpose of anodization in aluminum processing?
To increase the thickness and regularity of the aluminum oxide layer.
Aluminum is the most abundant metal in the earth's crust, making up _____ % of its composition.
Aluminum is the most abundant metal in the earth's crust, making up _____ % of its composition.
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Match the following characteristics with the respective material:
Match the following characteristics with the respective material:
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What happens to aluminum alloys at high temperatures (200-2500C)?
What happens to aluminum alloys at high temperatures (200-2500C)?
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Aluminum maintains its strength at negative temperatures while retaining its ductility.
Aluminum maintains its strength at negative temperatures while retaining its ductility.
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What treatment is performed after anodization to minimize porosity in aluminum oxide layers?
What treatment is performed after anodization to minimize porosity in aluminum oxide layers?
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Which metallic element is NOT commonly used in food packaging?
Which metallic element is NOT commonly used in food packaging?
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Metal packaging materials have a high tendency to break compared to glass.
Metal packaging materials have a high tendency to break compared to glass.
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What are the properties of metallic bonds that contribute to the strength and flexibility of metals?
What are the properties of metallic bonds that contribute to the strength and flexibility of metals?
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Metal packaging has __________ thermal conductivity, allowing for efficient heat transfer.
Metal packaging has __________ thermal conductivity, allowing for efficient heat transfer.
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Match the following metallic materials to their specific usages:
Match the following metallic materials to their specific usages:
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What is a main disadvantage of metal packaging compared to glass packaging?
What is a main disadvantage of metal packaging compared to glass packaging?
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List two advantages of using metal packaging over glass.
List two advantages of using metal packaging over glass.
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What is the typical thickness range of aluminum foil?
What is the typical thickness range of aluminum foil?
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Metal packaging can interact with food only if the wrong type of can is selected.
Metal packaging can interact with food only if the wrong type of can is selected.
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Aluminum is the only metal suitable for making three-piece welded cans.
Aluminum is the only metal suitable for making three-piece welded cans.
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What two metals are commonly used for alloying aluminum?
What two metals are commonly used for alloying aluminum?
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Aluminum foil has excellent barrier properties to ______, gas, and aroma.
Aluminum foil has excellent barrier properties to ______, gas, and aroma.
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Which of the following statements about aluminum foil is true?
Which of the following statements about aluminum foil is true?
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Match the alloying metals to their effects on aluminum:
Match the alloying metals to their effects on aluminum:
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Recycled aluminum maintains its quality during the re-melting process.
Recycled aluminum maintains its quality during the re-melting process.
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Aluminum foil is often laminated onto plastic film or paper to provide a barrier against ______, oxygen, and moisture.
Aluminum foil is often laminated onto plastic film or paper to provide a barrier against ______, oxygen, and moisture.
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Which type of can is made using pre-coated, laminated and printed tinplate or TFS?
Which type of can is made using pre-coated, laminated and printed tinplate or TFS?
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Aluminum is the material used for making two-piece drawn and wall ironed (DWI) cans.
Aluminum is the material used for making two-piece drawn and wall ironed (DWI) cans.
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What is the main purpose of exhausting cans before double seaming?
What is the main purpose of exhausting cans before double seaming?
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The coating of metal coil or sheet is typically performed by __________.
The coating of metal coil or sheet is typically performed by __________.
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Match the following can types with their characteristics:
Match the following can types with their characteristics:
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What is a key factor that must be avoided during the filling process of cans?
What is a key factor that must be avoided during the filling process of cans?
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Organic materials are used solely for decorative coatings on metal containers.
Organic materials are used solely for decorative coatings on metal containers.
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What performs the function of achieving a vacuum condition in cans?
What performs the function of achieving a vacuum condition in cans?
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What is the main reason freezing filled cans should be avoided?
What is the main reason freezing filled cans should be avoided?
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Canned foods can remain satisfactory for consumption even after their minimum durability period.
Canned foods can remain satisfactory for consumption even after their minimum durability period.
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What common chemical reaction occurs due to electrochemical corrosion of iron?
What common chemical reaction occurs due to electrochemical corrosion of iron?
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The process of sealing foods in a container followed by heat treatment is called _____.
The process of sealing foods in a container followed by heat treatment is called _____.
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Which factor is NOT one of the main factors affecting the shelf life of canned foods?
Which factor is NOT one of the main factors affecting the shelf life of canned foods?
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Match the following terms with their descriptions:
Match the following terms with their descriptions:
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Tinplate does not need any lacquer when used for packing aggressive food products.
Tinplate does not need any lacquer when used for packing aggressive food products.
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Name one method used to minimize external corrosion in canned foods.
Name one method used to minimize external corrosion in canned foods.
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What is the role of tin in canned foods?
What is the role of tin in canned foods?
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High concentrations of tin in food can lead to gastrointestinal irritation.
High concentrations of tin in food can lead to gastrointestinal irritation.
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What is the legal limit of tin content in food products as per EU regulations?
What is the legal limit of tin content in food products as per EU regulations?
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High levels of __________ in food can make it unpalatable due to flavor and color changes.
High levels of __________ in food can make it unpalatable due to flavor and color changes.
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Which factor does NOT affect the rate of tin dissolution from the can surface?
Which factor does NOT affect the rate of tin dissolution from the can surface?
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Match the following substances with their effects or characteristics:
Match the following substances with their effects or characteristics:
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Name one effective method to limit tin dissolution in canned foods.
Name one effective method to limit tin dissolution in canned foods.
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The presence of chemical preservatives can accelerate tin toxicity.
The presence of chemical preservatives can accelerate tin toxicity.
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Study Notes
Metal Packaging
- Metallic elements have a compact chemical structure, resisting diffusion.
- They are malleable, allowing for various shapes.
- High thermal conductivity facilitates heat transfer.
- High electrical conductivity allows for electricity.
- Metal alloys are often used in food packaging, primarily based on aluminum, tinned steel, stainless steel, copper, and nickel.
- Aluminum alloys are commonly coated with tin, chromium oxides, or varnishes.
- Stainless steel is used for food contact applications (containers, vessels, utensils).
- Copper and cast iron are occasionally used for food contact purposes (e.g., dairy boilers, grill tools).
- Nickel is used as a sandwich layer between steel and tin.
- Lead is occasionally used for soldering.
- Copper is used for welding can seams.
Metallic Bonds
- Metallic bonds are responsible for the strength, malleability, and ductility of metals.
- Hammering or stretching can cause metal layers to slide, allowing the free electrons to re-arrange without disrupting the bond.
- Metallic bonds are responsible for high electrical and thermal conductivity, since the free electrons can move throughout the lattice of metal ions.
Distinct Advantages of Metal Packaging over Glass
- Good heat transmission, facilitating rapid heating and cooling.
- Lighter weight compared to glass.
- Resistant to breaking and physical damage.
- Impermeable to both light and air.
Container Designs
- The images show typical round-section food and beverage cans.
- The images show example handles and designs.
Steel (Raw Materials)
- Steel is a wide family of iron alloys with a low carbon content.
- Carbon acts as a binding agent.
- Higher carbon content correlates to higher tensile strength and brittleness.
- Low-carbon steel is frequently used in containers.
- Steel is typically coated to prevent interaction of the metals with food products.
Tinplate
- Tinplate is low-carbon steel coated with a thin layer of tin, improving corrosion resistance making it suitable for direct food contact.
- Organic coatings often coat the inside of tinplate, preventing interactions between the metal and food product.
Tin-Free Steels
- Tin-free steels are utilized in cases where tin is not needed or is cost-prohibitive.
- Cold-rolled steel coated with electrolytic chromium or chromium oxide is a desirable alternative.
- They offer resistance to heat, lacquer adhesion, and printing.
- Tin-free steels might be less resistant to acidic environments.
Polymer Coated Steels
- Polymer coatings are applied to tinplate or tin-free steels for better appearance, corrosion resistance and moisture barriers.
- Thermoplastic polymers are often used in such coatings.
Stainless Steel (Raw Materials)
- Stainless steel is an iron alloy with enhanced corrosion resistance, stemming from the high chromium content (minimum 11%).
- Chromium reacts with oxygen forming a protective chromium oxide layer.
- The uniform composition across the can material avoids needing further protective coating.
- Stainless steel is divided into three basic groups (Austenitic, Ferritic, and Martensitic).
- Austentic is important for food applications.
Aluminum (Raw Materials)
- Aluminum is a very abundant metal in the Earth's crust.
- It's a light-weight material with high energy requirements for production.
- Electrochemically, aluminum reacts readily with oxygen, forming a thin passivated oxide layer, thus protecting itself from corrosion.
Aluminum Properties
- Aluminum alloys' strength and ductility are maintained across temperature variations.
- High malleability and workability facilitate shaping and forming the metal.
Aluminum Drawbacks
- Aluminum is very expensive to manufacture and weld.
- It is less resistant to corrosion than steel.
Aluminum Foil
- Aluminum foil is made through rolling a sheet of aluminum alloy.
- It has excellent water, gas, and aroma barriers.
- It's lightweight and resistant to many foods, but reacts somewhat with acidic and/or salty foods.
- Its dead-fold property can lead to pinholes during handling.
Recycled Packaging Metal
- Both aluminum and steel-based materials can be re-melted and re-used, with no loss of quality, during the re-melting process.
Three-Piece Welded Cans
- These cans consist of a body blank and two ends.
- Steel is the primary material used in this type of manufacturing.
- Aluminum generally is not suitable for welding in this process.
Two-Piece Single-Drawn and Multiple-Drawn Cans
- Pre-coated, laminated, and printed tinplate or TFS is typically used in this process.
- The cans are drawn into different shapes.
Two-Piece Drawn and Wall Ironed (DWI) Cans
- Typically using uncoated tinplate, these cans undergo a heat process, making aluminum unsuitable.
- Specific steps are undertaken to form the end shapes and draw the cans into various shapes.
End-Making Process
- This process prepares and finishes the ends of the cans.
- Steps include preparing the end shells, converting them into easy-open ends, etc.
Coatings, Film Laminates, Inks
- Organic materials like coatings, films, inks, etc. are applied to create barriers and enhance the appearance of both the container and components.
- Coating and decoration are applied to different types of containers (e.g., 2- and 3-piece cans) prior to the forming operation.
- Coating application might be based on the form (i.e. flat, coil, or sheet), thus the processes differ.
Can Reception at Packers
- Inspection in the packing stage determines things such as dimensions, seam defects, presence, or lack of internal lacquer, presence of defects, quality, etc.
Filling and Exhausting
- Accurate and consistent filling is critical, avoiding damage to the can and contamination.
- Avoiding external contamination and maintaining an appropriate headspace (oxygen levels) in cans reduces the chances of corrosion.
Seaming
- Double-seam formation involves two separate processes on the can end and body.
- Key parameters, such as seam thickness, height, and overlap, are measured and tracked.
Heat Processing
- Sterilization typically ranges from 115°C to 135°C.
- Pasteurization occurs within the range of 90°C to 105°C.
- Temperature differences between the process and the can interior can lead to distortion issues.
Post-process
- Proper cooling using water prevents bacterial risks (e.g., botulism spores) and promotes rusting prevention.
- Proper drying prevents microbial growth and corrosion.
Container Handling
- Any defect on the container needs to be regarded as a critical concern.
- Seam areas are prone to contamination.
Storage and Distribution
- Temperatures and humidity levels must be managed to prevent condensation and further corrosion.
- Freezing conditions need to be avoided to avoid expanding issues.
- Physical handling needs to be careful.
Shelf Life of Canned Foods
- Canning method is crucial to food stability.
- Possible chemical reactions, color, flavor, and interactions with the containers can influence the shelf life of foods.
- Minimum durability refers to the time a product remains marketable during normal storage.
- Technical shelf life is the time a product remains fit to eat during normal usage.
- Different factors influence shelf life, including sensory quality (color, flavor), nutritional stability, and container/product interactions.
Corrosion
- Corrosion in metals typically involves two steps — an initial ionization by metal and subsequent electron transport through the material.
- Oxygen and other oxidizers are common corrosion facilitators.
- The resulting metal oxides are a key component in corrosion and rust formation.
Interaction between Can and Contents
- Tin protects the steel base-plate from corrosion.
- Lacquering is common to treat or prevent interactions between containers and contents, and in many cases, prevents dissolution of certain metals into food products.
Internal Corrosion
- This can emanate from mechanical damage as well as specific reactions between can and content.
- Inadequate lacquers or cracking in lacquers can significantly increase the chances of internal corrosion.
Stress Corrosion Cracking
- Stress corrosion cracking, when a particular environment allows for a more rapid corrosion, most commonly due to external stresses in metals, internal stresses from cold working, and certain types of metals.
- Determining the starting points for cracks can be very difficult—this process is most common in the beaded part of canned metal containers.
Environmental Stress Cracking Corrosion of Aluminum Alloy Beverage Can Ends
- This type of corrosion can develop in specific situations in can ends.
- Such issues can appear at pull-tab or stay-on-tab ends.
- Handling and drying containers before storage can reduce the risks of contamination.
Sulfur Staining
- Sulfur compounds from food products can react with the can metal
- A reaction that leads to sulfide stains.
External Corrosion
- Rusting is a type of external corrosion.
- Corrosion occurs due to condensation, temperature fluctuations, and the presence of moisture, oxygen, and certain metal elements.
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Description
Test your knowledge on the properties and characteristics of aluminum and stainless steel. This quiz covers topics such as anodization, corrosion resistance, and metallic bonds. Perfect for students in materials science or engineering courses.
